Effects of the safeners CGA 154281, oxabetrinil and fenclorim on uptake and degradation of metolachlor in corn (Zea mays L.) seedlings

Summary. The influence of three crop safeners on the uptake and degradation of 14 C‐metolachlor was investigated in two corn varieties. Following application of herbicide and safener together to seedling shoots the concentrations of non‐metabolized 14 C‐metolachlor in the tissues was found to be lower in the tolerant variety LG 9 than in the susceptible variety 211A. The difference between varieties was due to differences in both uptake and degradation of 14 C‐metolachlor. Following shoot application most of the radioactivity was retained in the coleoptile and the mesocotyl. Two hours after application 95% of the herbicide had been degraded in coleoptiles and mesocotyls, whereas approximately 20% of non‐metabolized 14 C‐metolachlor was present in the enclosed developing shoot leaves. In both corn varieties the safener CGA 154281 caused a substantial lowering of tissue levels of parent 14 C‐metolachlor. This was primarily due to an enhanced degradation. Glutalhione‐ S ‐transfer‐ase (GST) enzyme activity in shoot tissues was found to be enhanced in both varieties by CGA 154281. Oxabetrinil and fenclorim were less effective than CGA 154281 both in reducing tissue levels of non‐metabolized 14 C‐metolachlor and in enhancing GST activity in either variety.